"James Nicoll" wrote in message ...
No. For one thing, there's a real problem coming up with a gas
giant mass of just heavy elements. The Sun, for example, has the following
elemental abundances:

Element % of mass

Hydrogen 91.2
Helium 27.1
Oxygen 0.97
Carbon 0.40
Nitrogen 0.096
Silicon 0.099
Magnesium 0.076
Neon 0.058
Iron 0.014
Sulphur 0.04


A Solid Jupiter made of silicon, say, is equal in mass to the
entire supply of silicon in the Sun and raises questions like 'what
happened to all the hydrogen that should be associated with a lump
of Si that large?'


Fair enough. Of course we could imagine it's silicon dioxide with lots of
iron, which helps a bunch but possibly not enough. Put it in orbit around
a star with a higher concentration of heavy elements?

How about metallic hydogen? (that's mostly a joke).

More seriously, water might be a good choice. It's abundent, less likely to
be lost from the atmosphere than H2, and can make some 'interesting' ice
forms down where the pressure gets high. A water planet is more dense
than a H2 planet.

I can imagine a planet where the loose H2 got burned away but the H20
remains.

Interestingly, ice-XI and ice X both have a density greater than 2.5